a bash script to change postgresql user password
Easier if you use sudo:
sudo -u postgres psql -U postgres -d postgres -c "alter user postgres with password 'password';"but it's possible with su too, this should work:
su - postgres -c "psql -U postgres -d postgres -c \"alter user postgres with password 'password';\""I've used outer double quotes and escaped the inner double quotes so they pass through as part of a single call argument to su and get unescaped by the shell so the actual query text gets passed as a single arg to psql including the single-quoted password.
One of the reasons sudo is easier for this is that it uses a smarter way of executing the subprocess instead of running a second shell instance to do it. You need one less layer of shell metacharacter escaping.